The present invention relates to a data symbol reader used to read and decode data symbols such as two dimensional tessellated code symbols.
Recently, point-of-sale (POS) systems employ data symbol readers in order to scan bar-code labels on products, thereby increasing the speed at which products can be processed through a check out of a store. However, bar-code labels store data in only one dimension (i.e., the scanning direction) and therefore can only store a limited amount of data.
To overcome the problem of limited data storage, a new type of symbol which stores data in two directions has been proposed. This new type of symbol (hereinafter referred to as a two-dimensional symbol) uses a tessellated pattern to store the data.
When one dimensional bar-codes are used, the angle between a reference surface of the bar code and the data symbol reader is not critical, since a relatively simple scanning process is employed. Similarly, the distance between the reference surface of the bar-code and a light receiving portion of the data symbol reader is also not critical, since the simple scanning process is used.
However, if this simple scanning method is used to read two dimensional tessellated codes, the received image may be distorted and the wrong information may be decoded. Therefore, the positioning of the data symbol reader is critical if the proper information is to be decoded. Further the distance from the tessellated code to the light receiving portion of the encoded system must be kept constant in order to properly decode the tessellated code.
Thus, if this scanning system is to be used to scan a two-dimensional symbol, the positioning of the data symbol reader with respect to the reference plane of the symbol must be constant. This may prove difficult if the two-dimensional symbol is not placed on a perfectly flat surface.
In order to overcome this problem, an area sensor has been developed for the data symbol reader in order to read the two-dimensional symbols. The area sensor scans the entire tessellated pattern simultaneously. An example of a known data symbol reader employing an area sensor is shown in FIG. 11.
FIG. 11 shows a conventional data symbol reader 100 which consists of a main body 101 and a reading head 103. The reading head 103 houses a reading module 102. FIG. 12 shows a top view of an opening 104 formed in the reading head 103. The opening 104 is delimited by an rectangular wall 105 of the reading head 103. A reading area 36 is defined within the opening 104 and corresponds to an area in which the data symbol reader may be read.
As shown in FIG. 12, if a part of the data symbol 38 is overlapped with the rectangular wall 105, but inside an outer peripheral surface 106 of the reading head 103, proper decoding of the symbol 38 will not be possible.